The present invention relates to magnetic drive couplings, and more particularly to couplings which can accommodate and provide for passing gas lines, fluid tubes, electrical wires, or other conduits or members therethrough.
Critical component positioning requirements can sometimes cause a conflict between those components and a magnetic drive associated therewith. For example, in a biological reactor vessel having an internal magnetically driven mixer, it may be necessary to have a fluid conduit enter the vessel on the axis of rotation of the internal parts. In such a case, the external magnetic drive may have to be spaced a considerable distance from the vessel wall. However, the large air gap caused by spacing the drive at this distance means there will be significant flux leakage in the magnetic coupling. The torque transmission capability of the magnetic drive can accordingly be drastically reduced.
Many prior art magnetic drive mechanisms have driving and driven members which are separated by a gap. Some of these are provided with magnetic coupling elements which conduct some of the magnetic flux.
U.S. Pat. No. 2,638,558 (Rankin, issued May 12, 1953) shows a stationary stainless steel sheet 19 between drive magnets 24 and driven magnets 27. Means are provided for directing a flow of cooling fluid to the steel sheet 19 to overcome eddy current induced heating caused by the movement of the magnets.
U.S. Pat. No. 2,768,316 (Neiss, issued Oct. 23, 1956) shows circular arrays of magnets on driving and driven members.
U.S. Pat. No. 3,011,842 (Norris, issued Dec. 5, 1961) shows magnetic bearing rings separated by steel balls. The steel balls are kept evenly spaced by the effects of the magnets.
U.S. Pat. No. 3,378,710 (Martin, Jr., issued Apr. 16, 1968) shows (FIG. 17) driven pole pieces 109 and spacers 108 between stationary magnets 97 and moving magnets 112. The configuration of FIG. 18 shows stationary magnetizable radial bars 119 between rotating magnets.
U.S. Pat. No. 3,382,386 (Schlaeppi, issued May 7, 1968) discloses stationary soft magnetic coupling elements 3-6.
U.S. Pat. No. 3,433,465 (Szpur, issued Mar. 18, 1969) shows (FIGS. 2, 4, 9, 10, and 12) flux concentrating shoes 62, 147, and 194. (See col. 3, lines 21-34.)
U.S. Pat. No. 3,570,819 (Rosinger, issued Mar. 16, 1971) shows (FIG. 21) a dual stirring arrangement in which a magnet 182, which stirs liquid in an outer vessel, is located between a driving magnet 183 and another driven magnet 186.
U.S. Pat. No. 4,209,259 (Rains et al., issued June 24, 1980) discloses (FIGS. 1, 4, and 5) a high power, high torque apparatus using circular magnet arrays.
U.S. Pat. No. 4,498,785 (de Bruyne, issued Feb. 12, 1985) shows a magnetic stirrer in a bioreactor-type apparatus (see cols. 1 and 2 ).
German Offenlegungsschrift No.27 09 365 (Wik, published Sept. 15, 1977) shows (FIG. 5) mu-metal discs P.sub.1, P.sub.2 for concentrating flux between drive and stirring magnets.
Nowhere, however, do these patents teach or suggest a magnetic drive which provides clearance for a fluid conduit or other essential component without causing appreciable loss of the torque transmission capability of the coupling.
A need therefore remains for a means for extending the usefulness of magnetic drive couplings when relatively large gaps have to be tolerated because of other constraints. Ideally, such a means will be especially effective at reducing the reluctance of such a gap, concentrating the magnetic flux in the interface between the driving and driven members of the magnetic drive, reducing the torque diminishing effect of such a gap, and enhancing the torque transmitting capability of the magnetic drive coupling.